Making disposable electric devices

ABSTRACT

A method for making disposable electric devices, such as flashlights, which includes providing a casing having one or more battery compartments; coating one or more surfaces of each compartment with an electrode overlay, such as zinc; coating one or more surfaces of each compartment with another electrode overlay such as carbon; providing serial or parallel electric connection between the compartments; filling the compartments with a battery mix; inserting the operative electrical elements of the device, such as a bulb and lens assembly, in connection with the electrodes and sealing the device.

United States Patent Appl. No.: 1 13,163

Related 1.1.8. Application Data Division of Ser. No. 844,592, July 24,1969, Pat. No. 3,601,601.

U.S. Cl 29/592, 136/175, 136/131 Int. CL. H0lm 1/00 Eilenberger 11mm 19,1973 [54] MAKING DISPOSABLE ELECTRIC DEVICES 3,007,994 1 [/1961 Urry136/126 2,745,774 5/1956 Reid 117/216 [75] Inventor Stanley Mmdlemwm3,400,020 9/1968 comm, et a1. 136/120 Conn' 2,931,894 4/1960 Bruehl240/1061 [73] Assignee: Progressive Products Corporation, 1

Kensington, Conn. Primary Examiner-Charles W. Lanham 1 AssistantExaminer-D. C. Crane [22] Flled' 1971 Attorney-Russell & Nields 1 57ABSTRACT A method for-making disposable electric devices, such asflashlights, which includes providing a casing having one or morebattery compartments; coating one or more surfaces of each compartmentwith an electrode overlay, such as zinc; coating one or more surfaces ofeach compartment with another electrode overlay such as carbon;providing serial or parallel electric connection between thecompartments; filling the compartments with a battery mix; inserting theoperative electrical elements of the device, such as a bulb and lensassembly, in connection with the electrodes and sealing the device.

16 Claims, 16 Drawing Figures PATENTED g 13. T39 ,464

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STANLEY D. EILENBERGER ATTORNEYS 1 MAKING DISPOSABLE ELECTRIC DEVICESCROSSREFERENCE TO RELATED APPLICATION This application is a divisionalapplication of my copending application, Ser. No. 844,592, filed July24,

1969, now US Pat. No. 3,60l,60l.

BACKGROUND OF THE DISCLOSURE mize the amount of mix which ban beencased. See for example US. Pat. Nos. 2,561,532; 2,494,265; and2,794,904. Such devices, however, apparently have not realizedwidespread commercial success. Recently a disposable flashlight batteryhas achieved commercial success, but this is of the design illustratedin expired U.S. Pat. No. 2,401,349, wherein two battery cells ofordinary design are encased in a plastic container having the customarybulb and wiring. Indeed, this device is hardly more than a conventionalflashlight, having a plastic case, that becomes permanently useless assoon as the batteries expire.

The present invention results in an electrical device having a very highyield of battery mix per unit volume, and which is truly disposable inthe sense that the total cost of the unit is competitive with the costof ordinary cell batteries capable of delivering similar electricaloutput. The low total cost is due in part to the present method, whichis readily adapted to high-speed automated procedures.

It is therefore the major objective of the invention to i provideelectrical devices in which a battery mix is encased within the devicein a high yield per unit volume. Another objective is to provideelectrical devices, of long life, having a battery mix encased by thedevice casing. It is a further objective to provide such a method. whichentails a series of simple process steps capable of high-speed automaticperformance in order that a minimum of time and of hand-assemblyoperations is necessary. Other objectives, as well as advantages, of theinvention will become apparent as the invention is further describedbelow.

DESCRIPTION OF THE DRAWINGS The invention isillustrated in the attacheddrawings, which serve to illustrate the present method. These drawingsinclude:

FIG. I, a cross-sectional view in side elevation of a flashlight casehaving two compartments, with two controde overlay of carbon have beenapplied to the exposed zinc surfaces, and after battery mix has beenadded;

FIG. 4, across-sectional view along lines 44 of FIG. 3;

H (6) filling the battery compartment(s) with a battery FIG. 5, a sideelevation view, partly in cross-section, of the case after paper washersand an end seal of wax have been put in place;

FIG. 6, a side elevation view, partly in cross-section, of the caseafter the contacts have been given their final shape and the lamp andlens assembly have been attached;

FIGS. 7 and 8, cross-sectional views in end elevation showing analternative case arrangement in two pieces with interlocking means;

FIGS. 9 and 10, elevation views partly in cross ment having conductivemeans between opposite walls,

eight of which are used in the case arrangement of FIG. 11;

FIG. 13, a cross-sectional view showing in elevation another alternativecase arrangement wherein the contacts need not extend into the batterycompartments;

FIG. 14, a cross-sectional view along lines 14-14 of FIG. 13;

FIG. 15, a cross-sectional view of the case of FIGS. 13 and 14, afterthe zinc and carbon electrode overlays have been applied, after thepaper barriers and battery mix have been inserted, after the sealingmeans of FIGS. 9 and 10 has been inserted, and after contacts have beeninserted; and

FIG. 16, a cross-sectional view partially broken away along lines 1616of FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION The present invention includes anovel method of making disposable electric devices which is at oncesimple and efficient. In brief, the method involves incorporating in acertain way battery mix and operative electrical elements in a casing,the structure of which will of course vary depending upon the ultimateuse of other, similar devices, such as night lights, candleY sticks,bicycle lights or horns, cigarette lighters, desk calendars, alarms, andthe like.

The present method includes in combination the following steps: (I)providing a casing for electrodes, battery mix and the operativeelectrical elements of the device, preferably composed of a strong,inert plastic material, and containing at least one battery compartment;(2) inserting two electrical contacts into the cas ing to provideconductive means from the battery compartment(s) to the electricalelements; (3) coating partly or completely at least one wall of eachbattery compartment with an electrode (e.g., zinc) overlay and providingelectrical contact between an overlay and at least one of the electricalcontacts; (4) coating partly or completely at least one other wall ofeach battery compartment with another electrode (e.g., carbon) overlayand providing electrical contact between that overlay and one of theelectrical contacts: (5) preferably, coating substantially completelythe former (zinc) overlay(s) of each compartment with a paper barrier;

mix; (7) sealing the battery compartment(s); (8) and attaching andelectrically connecting the operative electrical elements to the twoelectrical contacts.

The particular order in which all of the above steps are performed isnot critical, but it is preferred that steps 1 (3), (4), (5), (6) and 7are performed at least in part in that order. Step (2) can be performedwhenever it is convenient to insert the contacts in conductiverelationship with the compartment(s). Further, in order to ensure goodelectrical contact, it may be preferable to coat two or more walls ofeach compartment with a zinc overlay and at the same time to provideelectrical contact between electrical contacts and the two differentzinc overlays, and then to coat one zinc overlay of each compartmentwith a carbon overlay. This procedure is illustrated in the drawings andwill be described fully below. In addition, where a plurality of batterycompartments is to be used, it is of course necessary to provideelectrical contact between the zinc overlay of one compartment and thecarbon overlay of the next. Various ways of simply achieving suchcontact are described hereafter.

The casings for the present electrical devices are preferably made of astrong, inert plastic. The material should be strong enough to withstandthe impact of normal usage, which inevitably would result in droppingfrom heights up to several feet, without breaking or otherwise leakingthe battery mix. And it must be chemically resistant to the battery mix,i.e., noncorroding or inert. Of course, the casing should not beelectrically conductive to the extent of defeating its purpose. Severalwell-known plastics have suitable properties; among them are mediumorhigh-impact polystyrene, phenolics, vinyls, polyamides, polycarbonatesand similar plastics. The casings may be fabricated by any suitabletechnique, many of which are well known, such as compression orinjection molding.

If the electrodes are to be applied by spraying, it ordinarily isnecessary to treat the casing surface, for example by sand blasting, torender it capable of adhering with the sprayed electrode film. Finally,if the case is originally in two pieces, or more, they must be sealed toprevent leakage, preferably by ultrasonic sealing. Case sealing is mostconveniently performed after the electrode overlays are applied, and maybe done before the battery mix is added and the battery compartments aresealed. If ultrasonic sealing is employed, the edges must be clean,which would be achieved also by sand blasting. One of the advantages ofthe present method is its speed, which in ordinary operation issufficient to ensure that the casing, after the original sand blasting,remains clean until sealing. The electrode overlays are formed fromsuitable electrode materials. A preferred .anode material is zinc, whichmay be applied by any suitable method, such as spraying, coating orotherwise applying the electrode layer. The term overlay, as used here,is not intended to limit the method of application, for example, tospraying, although this method is a preferred component of theinvention. The overlay may be applied to the battery compartmentsurface(s) even as a preformed layer, provided that in use it is inintimate contact with the surface(s).

A zinc overlay preferably is 99.9 percent pure, and should preferably befree of iron, tin, arsenic, antimony, magnesium, copper and otherdetrimental impurities. Because of the nature of this invention,impurities which affect only the mechanical properties of zinc, such aslead or cadmium, may be tolerated, but

those which adversely affect electrical properties, in particular ironand copper, should be avoided. A zinc overlay may be applied by flamespraying, which is preferred, arc spraying, sputtering or plasmaspraying, methods which are generally known to those of the art, as wellas by electrodeposition and vacuum metallizing. Flame spraying is apreferred method in part because it results in a high surface area forthe zinc, which is advantageous. Since, unlike ordinary battery cells,the zinc is not used for mechanical strength, the zinc overlay need onlybe thick enough to provide good potential and a complete reaction whenthe battery is exhausted, although for practical reasons some excess isusually desired. An overlay thickness of about 0.009 inch is adequate,and a thickness in the range of about 0.0030.02 is normally suitable.

The cathode ordinarily used in conjunction with zinc anodes is, ofcourse, carbon. A carbon overlay may be applied by any of severalsuitable methods. In this invention the carbon overlay preferably isapplied from what has become to be known to the art as an electricallyconductive carbon dispersion, a dispersion of fine carbon particles in asuitable vehicle, e.g., alcohol or trichloroethylene. Preferably, acarbon overlay is applied as a pressure spray, sometimes referred to asairless, in a thickness of about 0002-0005 inch, or more. Since a carbonoverlay, expecially in this thickness range, is a poor electricalconductor, it is preferred to apply a zinc overlay beneath the carbonelectrode, so that conductivity is needed only through the carbonoverlay thickness, and not along its length. If this is done, however,it is important that the carbon layer on top of the zinc be continuous,with no discontinuities, in order that contact between the battery mixand the zinc sublayer be avoided.

A preferred method of ensuring a continuous carbon layer on a zincsublayer is to apply the carbon with a resin binder, although thisapproach may make difficult spray application. Alternatively, the carbonmay be applied as a continuous, preformed film on a substrate of carbonon a vinyl sheet to form a duplex electrode.

As will be apparent from the description hereafter, the zinc and carbonoverlays are applied to one or more walls of the battery compartments,but not to all of the wall surfaces. Hence, it is necessary whileapplying the overlays by any of the spraying methods to mask those wallsnot to be covered, preferably with a material to which the overlay willnot adhere, such as, for example, zinc, glass or chrome-plated steel.

There is no intention to limit this invention to the electrode overlayshere described in detail, i.e., zinc and carbon. Equivalent electrodematerials, such as magnesium or nickel-cadmium, may also be used, withsuitable modification to the battery mix composition and method ofoverlay application, these modifications being within the ordinary skillof the art. It is desirable to interpose' a barrier between the zincelectrodes and the battery mix, to prevent chemical reaction between themix and the zinc. This barrier may be a gel of cereal paste, such as amixture of cornstarch and flour which may be directly applied to thezinc anode by spraying or other means, or a gel-coated paper.Alternately, this paste may be prepared from such materials as locustbean flour or guar flour. The purpose of this gel is to provide a thinfilm between the electrolyte and the zinc anode. Paper coated withcereal paste, usually about 0.005 inch thick is preferred. When wettedby the electrolyte the coating becomes conductive for electric currentbut prevents chemical action between the ammonium chloride and the zinc.The barrier should be continuous and sealed at the edges, if contactbetween the zinc and mix is to be avoided.

The composition of the battery mix is not critical, many differentsuitable compositions being wellknown; some are described in theliterature and some are trade secrets of others. A typical compositionwould contain about 55-65 percent manganese dioxide, 5-25 percentgraphite or acetylene black, 8-15 percent ammonium chloride, 0.5-4percent zinc chloride, and -15 percent water. Equivalent ingredientsmay, of course, be substituted for the ingredients of the abovecomposition, and equivalent compositions are also known and may be used.

Inhibitors to reduce gassing, such as mercuric chloride or potassiumdichromate, may be added to the battery mix. Mercuric chloride ispreferred unless the device is to be used at elevated temperature, andmay be added in a concentration of up to 0.1 percent, or even more.Since the mercuric chloride forms an amalgam with zinc, therebyweakening the metal, ordinarily it is used only in small amount, usuallyabout 0.025 percent. Here, however, such restriction is not so critical,since the zinc is not needed for mechanical strength.

With reference to the drawings, FIGS. 1 and 2 show a flashlight casing1, composed of a strong, inert plastic material, having outer walls 2, acutout 3, designed to receive a switch button not shown, a centerdividing wall 4, and recessed tracks 5 and 6. The casing walls definetwo battery compartments 7 and 8 having wall surfaces 7a-e and Sa-e.Inserted into recessed tracks 5 and 6, respectively, are preformedelectrical contacts 9 and 10.

FIGS. 3 and 4 show the device after several further steps of the methodhave been performed, as follows.

The first step is the application of zinc overlays Ila-e, by a methodsuch as flame spraying, to contacts 9 and 10, wall surfaces 7d and 8a,and to frontend surface 12 of center wall 4. The purpose of this lastzinc overlay lle is to provide electrical contact between batterycompartments 7 and 8. Zinc overlays 11a and 110 ultimately are to be theanodes of the two battery cells to be providedin compartments 7 and 8,while overlay 11b is to provide contact between overlay lle and acathode, and overlay 1 1d is to provide contact between contact 10 andanother cathode. While the zinc overlay is being applied, walls 7b, c,e, and 812, c, e, are masked, in order to restrict application to thedesired areas.

The next step of the method, shown in FIGS. 3 and i 4, is theapplication of carbon overlays l3a-b, by spraying, for example, on zincoverlays 11a and 11c, respectively. These carbon overlays provide thecathodes for the two battery cells. While the carbon overlay is beingapplied, walls 7b, 0, e and 8b,'c, e, as well as zinc overlays 11b andd, are masked, in order to restrict application to the desired areas,zinc overlays 11a and.

cation of paper barriers l4a-b on the remaining exposed zinc overlays11b and lid of the battery compartments; and the addition of battery mix15 to compartments 7 and 8. FIG. 5 shows the device after paper washersl6 and wax seal 17 are applied to provide an airtight seal of thebattery compartments.

The next steps, shown in FIGS. 3 and 4, are the appli- After the batterycompartments have been sealed, 1

the electrical elements may then be incorporated into the device, andthe remaining steps of the method carried out. First, as shown in FIG.6, contacts 9 and II) are formed into their final shape, then lampassembly 18, consisting of lamp l9 and reflector 2%, is inserted intothe casing 1 against shoulder 121i. The lamp assembly may be aseparate'subassernbly made by a light press fit of lamp flange 22 intocollar 23 of relfector 12ft. After insertion, center contact 24' of lamp11%" is permanently connected to contact at nipple Switch an operates,by lateral sliding, to engage end 2'7 or contact 9 with lamp shell 28oflamp 3119, thereby completing the circuit and activating the lamp.After lamp assembly 118 is inserted, finally, lens assembly 29 isinserted to form a tight press fit with casing l at wall 30. Preferablythe flashlight device is then sealed to prevent disasscmbly,

and it is possible, if desired, to form a waterproof seal joinedtogether after the various overlays are applied,

as described above for casing. l, to the inner surfaces of walls 34 and35 and to both surfaces of center wall 32, by inserting peripheral. edge36 and center-wall edge 37 of the top and center wall into recessedperipheral groove 38 and center groove 39 respectively, with suitableadhesive means not shown, for example by ultrasonic sealing.

FIGS. 9 and 10 illustrate an alternative sealing mean for the batterycompartments. This type of seal is preferred because it alleviates thebuildup of by-product gases, principally hydrogen, of the electricdischarge of the battery. Preferably the sealing means, consisting ofmolded seal 40, having an aperture 41, and backing sheet 42, is composedof a plastic material permeable to hydrogen, in order to vent such gasthrough the backing sheet 42 and aperture 41, and substantially imtpermeable to water vapor, in order to retard drying of the battery mix,which would deactivate the battery. Such plastic material includecertain polyvinyl chlorides; low density polyethylenes, such as DINl-Idiameter of aperture may be about inch. Preferably the backing sheet 42is heat s-ealed to the back of molded seal40, or alternatively the twomay be molded together as a single molded seal, not shown.

FIGS. 11 and 12 illustrate an alternative battery cell arrangement in acasing having eight battery compartments. FIG. 11 shows the main casing43, consisting of,

side walls 44 and 45, end wall 46 and center wall 47. FIG. 12 showsdetail of a separator wall 49, provided with connector 50 for electricalcontact between the opposite sides of the wall. The eight compartments48a-h are formed by inserting eight separator walls 49, the connectionbeing between tongue 51 of the separator walls and grooves 52 a-h of theside walls 44 and 45 of casing 43, and between tongue 53a-h ofcenterwall 47 and grooves 54 of the separator walls 49.

The coating of the surfaces of casing 43 with the various overlays issomewhat complicated by the presence of so many compartments. Initially,surface 46a of the end wall is coated with a zinc overlay and surface46b, with a carbon overlay, and an electrical contact 55 is providedbetween these two end wall overlays. Then six separator walls 49, havinga carbon overlay on one side and a zinc overlay on the other, areinserted, in the locations between tongues 53b, 0, d, f, g and h andgrooves 52 b, c, d,f, g andh, shown in FIG. 11, as above described.Finally, a separator wall 49, having a carbon overlay on its interiorwall, is inserted between tongue 53a and groove 52a, and anotherseparator wall 49, having a zinc overlay on its interior wall, isinserted between tongue 53e and groove 52e. Contacts (not shown) similarto contacts 9 and 10, used in casing 1 above, may then be connected tothe connectors 50 or the last two separator walls 49 and to the lampassembly in the conventional manner.

FIGS. 13-l6 illustrate an alternative flashlight device, prepared by amethod somewhat different from that used as illustrated in FIGS. 1-6.With reference to FIGS. 13 and 14, battery case 56 is provided with sidewalls 57 and 58, end wall 59 and center wall 60, and contains twobattery compartments, 61 and 62. In the forward part of the case, aheadof the battery compartments, are recessed tracks 72 and 73, for theinsertion of contacts. The battery compartments have wall surfaces 61a-eand 62a-e.

FIGS. and 16 illustrate the battery case 56 of FIGS. 13 and 14, afterthe battery compartments have been filled and sealed and contactsinserted, but before the electrical elements have been incorporated. Themethod is first to coat surfaces 61a, 61d, 62a and 62d with anelectrode, such as zinc by the manner described above, to form overlays63a-d; to coat zinc overlays 63a and c with the second electrode,carbon, to form overlays 64a and b; and to cover the remaining zincoverlays 63b and d with paper barriers 65a and b. Connection betweenbattery compartments 61 and 62 is again provided by extending the zincoverlay 63e between overlays 63b and c. In addition, the application ofzinc overlay is extended beyond the battery compartments into theforward part of the case by conducting overlays 66a and b on forwardsurfaces 67a and b of case 56. With the various overlays in place,battery mix 68 and washers 69 are added, and hydrogenpermeable sealingmeans 70 (similar or identical to that illustrated in FIGS. 9 and 10) isforce-fitted against shoulder 71, and held in place in part by the ends72a and 73a of recessed tracks 72 and 73. This sealing means 70 providesa seal for the battery compartments that is permeable to hydrogen andsubstantially impermeable to water vapor. After sealing of the batterycompartments, contacts 74 and 75 are inserted into recessed tracks 72and 73, in intimate conducting contact with overlays 66a and b,respectively. The electrical components of the device, i.e., the switch,lamp and lens assembly, not shown, may be subsequently inserted in amanner similar to that used for the device earlier described.

It is apparent that in the device just illustrated in FIGS. 13-16 zincoverlays are applied directly onto the outer walls and extended beyondthe battery compartments into the vicinity of the operative electricalelements, and contact made there between the elements and the zincoverlay. This arrangement may be preferred, expccially where aneffective seal may be difficult to maintain due to the extension of thecontacts into the battery compartments. In any case, this latterprocedure should be deemed equivalent to the procedure of insertingcontacts into the battery compartments shown in FIGS. I-6.

It will be evident that devices other than flashlights, or flashlightsor" different construction, may be similarly prepared by the presentmethod, perhaps if desired by altering the dimensions and shape of thecase, and by employing suitably different operative electricalcomponents.

A number of variations of the above devices are possible still withinthe present method. As sometimes desired with batteries, it is possibleto provide for the release of pressure due to the formation of gasduring the battery discharge. This may be accomplished by substituting agas-permeable, liquid-impermeable seal for the wax seal, as abovedescribed. It also may be accomplished by the use of inhibiters, asabove described, or by employing an expansive seal, made for example ofelastic material, in place of the customary seal. Alternatively, aconventional gas vent may be employed to avoid the problem of gaspressure buildup.

The above specification has described preferred embodiments of theinvention, namely various two-cell and eight cell disposableflashlights. There is no intention to limit the invention to theillustrated embodiments, which is applicable as well to others.

I claim:

1. A method for making electrical devices, which comprises providing astrong, inert casing having at least one battery compartment, coating atleast one wall surface of said compartment with a first electrodeoverlay while masking the remaining wall surfaces, coating at least onewall surface of said compartment with a second electrode overlay whilemasking the remaining surfaces, in a manner such that at least one wallsurface is covered with said first electrode overlay and at least oneseparate wall surface is coated with said second electrode overlay,filling said battery compartment with a battery mix to provide apotential difference between said first and second electrode overlays,sealing said battery compartment, and inserting operative electricalelements into the casing in connection with the electrodes.

2. The method of claim 1, wherein said first electrode overlay is zinc,and said second electrode overlay comprises a carbon overlay.

3. The method of claim 2, wherein said zinc overlay is applied by flamespraying, and said zinc overlay is coated with a barrier.

4. The method of claim 2, wherein said zinc overlay is applied to atleast two wall surfaces of said battery compartment and said carbonoverlay is applied thereafter to one of said wall surfaces covered withsaid zinc overlay.

5. The method of claim 2, wherein at least one electrical contact isinserted into said battery compartment along a recessed track, toprovide electrical connection with said operative electrical components,and a zinc overlay is applied to said contact.

6. The method of claim 2, wherein said zinc overlay is extended beyondsaid battery compartment into a forward compartment of said casing, andelectrical connection is there made with said operative electricalelements.

7. The method of claim 2, wherein said casing comprises at least twobattery compartments, and electric cal elements comprise a switch, alight bulb and a lens assembly.

9. The method of claim 1, wherein said casing is constructed of molded,high-impact polystyrene.

10. The method of claim 1, wherein said battery cornpartment is sealedby a sealing means permeable to hydrogen and substantially impermeableto water vapor.

11. A method for making electrical devices, which comprises providing astrong, inert, two-piece, plastic casing capable of being sealed andhaving at least one battery compartment, sand blasting said casing,coating at least one wall surface of said compartment with firstelectrode overlay while masking the remaining wall surfaces, coatingsaid first electrode overlay with a barrier, coating at least oneseparate wall surface of said compartment with a second electrodeoverlay, comprising a conductive overlay on said separate wall surfaceand a dissimilar overlay on said conductive overlay, while masking theremaining surfaces, in a manner such that at least one surface iscovered witha first electrode overlay and at least one separate surfaceis coated with a second electrode overlay, joining and sealing the twoparts of the casing by ultrasonic sealing,

filling said battery compartment with a battery mix to provide apotential difference between said first and second electrode overlays,sealing the battery compartment, and inserting operative electricalelements into the casing in connection with the electrodes.

12. The method of claim ll, wherein said first elec trode overlay iszinc, and said second electrode overlay comprises a zinc conductiveoverlay and a carbon dissimilar overlay.

13. The method of claim 12, wherein said zinc over lays are applied byflame spraying.

14. The method of claim 12, wherein said zinc overlays are applied atonce to at least two walls of each

2. The method of claim 1, wherein said first electrode overlay is zinc,and said second electrode overlay comprises a carbon overlay.
 3. Themethod of claim 2, wherein said zinc overlay is applied by flamespraying, and said zinc overlay is coated with a barrier.
 4. The methodof claim 2, wherein said zinc overlay is applied to at least two wallsurfaces of said battery compartment and said carbon overlay is appliedthereafter to one of said wall surfaces covered with said zinc overlay.5. The method of claim 2, wherein at least one electrical contact isinserted into said battery compartment along a recessed track, toprovide electrical connection with said operative electrical components,and a zinc overlay is applied to said contact.
 6. The method of claim 2,wherein said zinc overlay is extended beyond said battery compartmentinto a forward compartment of said casing, and electrical connection isthere made with said operative electrical elements.
 7. The method ofclaim 2, wherein said casing comprises at least two batterycompartments, and electric connection between said two compartments isprovided by a zinc overlay.
 8. The method of claim 1, wherein saidcasing is the external casing of a flashlight and said operativeelectrical elements comprise a switch, a light bulb and a lens assembly.9. The method of claim 1, wherein said casing is constructed of molded,high-impact polystyrene.
 10. The method of claim 1, wherein said batterycompartment is sealed by a sealing means permeable to hydrogen andsubstantially impermeable to water vapor.
 11. A method for makingelectrical devices, which comprises providing a strong, inert,two-piece, plastic casing capable of being sealed and having at leastone battery compartment, sand blasting said casing, coating at least onewall surface of said compartment with first electrode overlay whilemasking the remaining wall surfaces, coating said first electrodeoverlay with a barrier, coating at least one separate wall surface ofsaid compartment with a second electrode overlay, comprising aconductive overlay on said separate wall surface and a dissimilaroverlay on said conductive overlay, while masking the remainingsurfaces, in a manner such that at least one surface is covered with afirst electrode overlay and at least one separate surface is coated witha second electrode overlay, joining and sealing the two parts of thecasing by ultrasonic sealing, filling said battery compartment with abattery mix to provide a potential difference between said first andsecond electrode overlays, sealing the battery compartment, andinserting operative electrical elements into the casing in connectionwith the electrodes.
 12. The method of claim 11, wherein said firstelectrode overlay is zinc, and said second electrode overlay comprises azinc conductive overlay and a carbon dissimilar overlay.
 13. The methodof claim 12, wherein said zinc overlays are applied by flame spraying.14. The method of claim 12, wherein said zinc overlays are applied atonce to at least two walls of each battery compartment, and said carbonoverlay is applied thereafter to one of said walls of each compartmentcovered with said zinc overlay.
 15. The method of claim 11, wherein saidcasing is constructed of molded, high-impact polystyrene.
 16. The methodof claim 11, wherein said battery compartment is sealed by a sealingmeans permeable to hydrogen and substantially impermeable to watervapor.